Skip to content
CVE PROGRAM SOURCE RECORD7.8 High

CVE-2026-68398

ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF

Read JSON ↗CVE.org ↗
Status
Published
Published
Updated
Assigning organization
Linux

Description

In the Linux kernel, the following vulnerability has been resolved: ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path: l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan) It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences. The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe. But the internal struct channel is a separate allocation that ppp_release_channel() frees with a plain kfree(): close(data socket) -> pppol2tp_release() -> pppox_unbind_sock() -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch) For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit (no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips both ppp_disconnect_channel()'s synchronize_net() and ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace period. rcu_read_lock() in pppol2tp_recv() does not protect against a plain kfree(), so an in-flight ppp_input() on one CPU can dereference the channel just freed by close() on another CPU. The bug is reachable by an unprivileged user. Defer the channel free to an RCU callback via call_rcu() so the grace period fences any in-flight ppp_input(). The disconnect and unbridge teardown paths already fence with synchronize_net()/synchronize_rcu(); call_rcu() does the same here without stalling the close() path.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 to < 4e47f1ac188ece11d6fdabe44166a2776cc5bd4eaffected
  • ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 to < 110b765744b147c63882f5e9cb12931c5dc8d85faffected
  • ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 to < 4bb84e964ff0fe0a171c965362de72f9820dbce9affected
  • ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 to < 3ab32218d7182705dae5c86f13925f458072da2caffected
  • ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 to < c9574b8a8edeb4edd3ac6472c27ef7184bdb2baaaffected
  • ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 to < 06213c85d8c0994f786c093b8b2a517987943ca6affected
  • ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741 to < ec4215683e47424c9c4762fd3c60f552a3119142affected
  • d36e5ba7bbed5d7bd26e8609ffed503c2def401baffected
  • 9bcc0508576b2d50efd958f2ea1c5906749c2c89affected
  • c2984681fe15cfb803a9132aaaf1140ab20a72c1affected
  • 5803ecd7f6ac6f747582e775caa62ac9d0489261affected
  • 26f8819ddd10141ebe7bbce700fbab36bfa5f478affected
  • 3.2.99 to < 3.3affected
  • 3.16.54 to < 3.17affected
  • 4.4.225 to < 4.5affected
  • 4.9.225 to < 4.10affected
  • 4.14.182 to < 4.15affected

Linux Linux

Default version status: affected

  • 4.15affected
  • 0 to < 4.15unaffected
  • 5.15.216 to ≤ 5.15.*unaffected
  • 6.1.183 to ≤ 6.1.*unaffected
  • 6.6.148 to ≤ 6.6.*unaffected
  • 6.12.101 to ≤ 6.12.*unaffected
  • 6.18.42 to ≤ 6.18.*unaffected
  • 7.1.6 to ≤ 7.1.*unaffected
  • 7.2 to ≤ *unaffected

References